Looking back over the last century, there were two great coalition builders in presidential politics: FDR and Richard Nixon.

Franklin Roosevelt broke the Lincoln lock on the presidency that had given Republicans the White House in 56 of the previous 72 years. From 1932 to 1964, FDR’s party would win seven of nine elections.

Nixon broke through in ’68 and built the New Majority that gave the GOP the White House for 20 of the next 24 years.

The Nixon-Reagan coalition, however, has aged and atrophied.

In five of the last six presidential elections, the Democratic nominee won the popular vote. And no fewer than 18 states, including four of the most populous — California, Illinois, Pennsylvania, and New York — have gone Democratic in all six of those elections.

Also, four states crucial to victory and once regarded as reliably Republican — Florida, Ohio, Virginia, and Colorado — have turned purple.

The GOP is also facing a demographic crisis. White folks, who provide almost 90 percent of Republican votes in presidential years, are steadily shrinking as a share of the electorate.

Is Hillary thus inevitable?

With the cash she can raise and the support of the sisterhood, she may be able to clear the field in the run for the nomination. And in a general election, it is hard to see which Republican today could take 270 electoral votes from her.

Yet the lady has vulnerabilities. If elected, Hillary would be, at 69, the oldest Democratic president ever. Husband Bill was nearly a quarter of a century younger when inaugurated, as was Barack Obama.

Her book tour for “Hard Choices,” with her tale of woe about having been “flat broke” in 2001, revealed a queen of privilege wildly out of touch with the hard realities of life in Middle America in 2014.

Moreover, there is Clinton fatigue in the country and this capital. Americans under 30 never knew a time when she was not around.

Her memoir looks likely to be remaindered long before it earns her publisher anything near the $14 million advance she is rumored to have received. Somebody at Simon & Schuster is going to the wall.

And the Democratic left is pawing the turf.

Is her record in office impressive?

The most critical vote she cast in eight years in the Senate — to take America into war with Iraq — she now admits was a mistake. And it’s not an insignificant one, considering the disaster that is Iraq today.

Her record as secretary of state?

The most memorable moment was announcing the “reset” with Russia. How’s that working out?

Not only must Hillary answer for the failures that brought about the Benghazi massacre, and her absenteeism in its aftermath; but she must also defend a foreign policy that has left her country less respected on every continent.

While most Americans support President Obama’s decisions to end the U.S. wars in Iraq and Afghanistan, there is something about his leadership on the world stage that calls to mind the Carter era.